1. Field of the Invention
The present invention relates to an EGR valve having a three-tiered valve stem bearing configuration.
2. Description of the Relevant Art
Typical Exhaust Gas Recirculation (EGR) valves are used to control exhaust gas recirculated to the intake side of an internal combustion engine. The EGR valve generally comprises a valve, positioned by an actuator to meter the exhaust gas which passes through the valve. The actuator retracts the valve from a seat to increase recirculation of exhaust gas, and advances the valve toward the seat to reduce recirculation of gas. The seat is incorporated in a base that mounts the valve on the engine manifold.
Precise alignment of the valve relative to the valve seat is desirable since misalignment of the two components may create a path for gas leakage to the engine causing exhaust gas flow variability, and resulting in wear of the valve and seat. It is desirable to maintain the valve stem in precise, coaxial alignment with the valve seat through the use of a precision valve stem bearing. Such a bearing should, in addition to providing the desired alignment, operate to prevent exhaust gas from escaping from within the EGR valve about the interface with the valve stem and to minimize impingement of any escaping exhaust gas on the valve stem actuator. Contact of the actuator with the moisture laden exhaust gas may result in conditions affecting the optimal performance of the EGR valve.